June 2016

Concussion repercussions: Studies explore lower extremity effects

In the moment: Sports medicine

6ITM-sports-shutterstock_341730932sm-copyBy Jordana Bieze Foster

The adverse biomechanical effects of concussion can persist for up to two years, but short-term visual deficits may help identify athletes who are most at risk for gait-related effects, according to multiple studies presented in early June at the annual meeting of the American College of Sports Medicine (ACSM) in Boston.

Researchers from the University of Michigan in Ann Arbor found significant differences in stop-jump kinetics between eight young adults (three women) with a history of concussion (mean 2.4 years from injury) and eight young adults (five women) with no history of concussion.

The study participants performed a horizontal jump equal to 120% of leg length, landed on the dominant leg (all were right-leg dominant), and then jumped to the right or left based on instructions received before the task. For the leftward trials, the mean peak medio­lateral ground reaction force was significantly higher for the concussion group than the no-concussion group.

Although there were no significant between-group differences for the rightward trials for the initial 16 participants for whom data were presented, the researchers did see between-group differences for both directions once the number of participants reached 20, according to Andrew Lapointe, MS, a doctoral student in the university’s School of Kinesiology, who presented the results.

“These findings do support the body of evidence showing an effect of concussion on gait and that motor dysfunctions remain long after the acute injury,” Lapointe said.

The long-term kinetic effects observed by the Michigan researchers may in part explain the results of a US Army study presented at the ACSM meeting, in which soldiers who sustained a concussion were significantly more likely to sustain a lower extremity injury in the next two years than nonconcussed controls.

Investigators from the US Army Research Institute of Environmental Medicine in Natick, MA, reviewed medical encounter data for nearly 8000 soldiers who had no history of lower extremity injury before experiencing a concussion. Of those, 1892 suffered a lower extremity injury within two years postconcussion; this 24% injury rate was 52% higher than for 11,602 matched controls during the same two-year periods. The greatest between-group differences in lower extremity injury rate were seen during the first six months postconcussion.

Joseph Kardouni, MPT, research director of the Total Army Injury Health Outcomes Database, who presented the findings at the ACSM meeting, said that further analysis of the same database (not presented) suggests the inverse of the presented findings is also true: Risk of concussion is higher in soldiers who sustain a lower extremity injury than in uninjured controls.

“If you’re at risk of getting hurt, you’re at risk of getting hurt,” Kardouni said. “Perhaps some of the factors that lead to getting concussions are the same risk factors that lead to other types of injuries.”

Although a number of studies have reported gait-related effects of concussion, few have examined how to identify which athletes are most likely to develop gait alterations. Research from Boston Children’s Hospital, presented at the ACSM meeting, suggests a visual deficit test may help.

In 31 adolescents examined within three weeks of a concussion (mean, 10 days), the Boston investigators found that 19 presented with deficits related to the near point of convergence (NPC; the ability to clearly see a target moving toward the tip of the nose). Those with NPC deficits walked more slowly and with shorter strides than 12 concussed participants with normal NPC and 28 uninjured controls.

“Theoretically, if you can train the visual system, you might have better recovery in terms of gait,” said David R. Howell, PhD, ATC, a postdoctoral research fellow at the Micheli Center for Sports Injury Prevention in Waltham, MA, who presented the findings at the ACSM meeting.

Sources:

Lapointe A, Sosnowski A, Andrews E, et al. Landing kinetics differences in individuals with and without a history of concussion. Presented at the 2016 annual meeting of the American College of Sports Medicine, Boston, June 2016.

Kardouni JR, Shing TL, McKinnon CJ, et al. Risk for lower extremity injury following concussion: a retrospective cohort study in soldiers. Presented at the 2016 annual meeting of the American College of Sports Medicine, Boston, June 2016.

Howell DR, O’Brien M, Raghuram A, et al. Adolescents with convergence insufficiency exhibit gait stability deficits acutely after concussion. Presented at the 2016 annual meeting of the American College of Sports Medicine, Boston, June 2016.

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